The present invention relates to a control system for a motor, and more particularly to a control system for a motor that determines an offset correction value that accounts or compensates for a dynamic component of DC offset of measured phase current.
Permanent magnet synchronous motors (PMSM) generally have a relatively high efficiency, low inertia and a high torque-to-volume ratio. In a PMSM current controlled application, a relatively accurate measurement of phase current supplied to the PMSM is required. This is because any DC offset in the measured phase current supplied to the PMSM results in torque ripple in the output torque of the PMSM.
There are several factors that may influence the DC offset in the measured phase current. These factors include, for example, temperature variation with an analog to digital converter (ADC), temperature variation in a current amplifier, the DC offset out of the current amplifier, and the inherent offset of the ADC. There are two components of DC offset in the measured phase current, a fixed component and a variable or dynamic component. The fixed component may be accounted for using a relatively simple approach. Specifically, an offset measurement representing the fixed component of the DC offset in the measured phase current may be determined, and then incorporated into an offset correction value. However, the dynamic component may vary with time and temperature, and may not be accounted for using the same approach as the fixed component.